Balancing redox reactions in acidic solution

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1) ClO₃¯ + SO₂ ---> SO₄²¯ + Cl¯

2) H₂S + NO₃¯ ---> S₈ + NO

3) MnO₄¯ + H₂S ---> Mn²⁺ + S₈

4) Cu + SO₄²¯ ---> Cu²⁺ + SO₂

5) MnO₄¯ + CH₃OH ---> CH₃COOH + Mn²⁺

Answers to Probs. 1-5

6) Cr₂O₇²¯ + Fe²⁺ ---> Cr³⁺ + Fe³⁺

7) HNO₂ ---> NO + NO₂

8) H₂C₂O₄ + MnO₄¯ ---> CO₂ + Mn²⁺

9) O₂ + As ---> HAsO₂ + H₂O

10) NO₃¯ + I₂ ---> IO₃¯ + NO₂

Answers to Probs. 6-10

11) HBr + SO₄²¯ ---> SO₂ + Br₂

12) H₅IO₆ + Cr ---> IO₃¯ + Cr³⁺

13) Fe + HCl ---> HFeCl₄ + H₂

14) NO₃¯ + H₂O₂ ---> NO + O₂

15) BrO₃¯ + Fe²⁺ ---> Br¯ + Fe³⁺

Answers to Probs. 11-15

16) Cr₂O₇²¯ + C₂H₄O ---> CH₃COOH + Cr³⁺

17) MnO₄¯ + C₂H₄O ---> CH₃COOH + MnO₂

18) Zn + NO₃¯ ---> NH₄⁺ + Zn²⁺

19) NO₂ + H₂O --> HNO₃ + NO

20) S²¯ + NO₃¯ ----> NO + S₈

No answers are provided for Probs. 16-20

21) CuS + NO₃¯ ---> NO + Cu²⁺ + HSO₄¯

Answer to Prob. 21

Problem #22: Ru(s) + Cl¯(aq) + NO₃¯(aq) ---> RuCl₆³¯(aq) + NO₂(g)

Solution

1) Eliminate the Cl¯ for the moment:

Ru ---> Ru³⁺ + 3e¯
e¯ + 2H⁺ + NO₃¯ ---> NO₂ + H₂O

2) Multiply second half-reaction by 3 and add:

6H⁺ + 3NO₃¯ + Ru ---> Ru³⁺ + 3NO₂ + 3H₂O

3) Add in the chloride:

6HCl + 3NO₃¯ + Ru ---> RuCl₆³¯ + 3NO₂ + 3H₂O

4) Add in three more H⁺, if you wish:

6HCl + 3HNO₃ + Ru ---> H₃RuCl₆ + 3NO₂ + 3H₂O

Comment: good ole aqua regia to the rescue!

Problem #23: IO₃¯(aq) + I₂(s) ---> I₂(s) + HIO(aq)

Solution

1) Half-reactions:

10e¯ + 12H⁺ + 2IO₃¯(aq) ---> I₂(s) + 6H₂O
2H₂O + I₂(s) ---> 2HIO(aq) + 2H⁺ + 2e¯

2) Multiply bottom by 5, then add:

10H₂O + 5I₂(s) + 12H⁺ + 2IO₃¯(aq) ---> I₂(s) + 6H₂O + 10HIO(aq) + 10H⁺

3) Eliminate like items:

4H₂O + 4I₂(s) + 2H⁺ + 2IO₃¯(aq) ---> 10HIO(aq)

4) If you wanted to recombine:

4H₂O + 4I₂(s) + 2HIO₃(aq) ---> 10HIO(aq)

Problem #24: Someday!

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